1. Field of the Invention
This invention relates to a method and apparatus for winding a fin ribbon onto a rotating tube to form a heat exchanger. More particularly the present invention concerns a control for regulating various motor drives to allow for high speed heat exchanger manufacture.
2. Prior Art
A wound fin heat exchanger is formed by winding a fin ribbon about the outer surface of a cylindrical heat exchange tube to provide a heat exchanger. The ribbon is normally formed in an L-shape or U-shape having fin portions projecting upwardly and is wound about the tube with a flat base portion in heat exchange relation with the exterior cylindrical surface of the tube. The projecting fins promote the transfer of heat energy between a gas flowing over the exterior surface of the tube and a fluid flowing through the tube. The fin ribbon is typically narrow in thickness and may be made of any heat transfer material although aluminum has been found particularly advantageous.
Various methods of applying fin ribbon to the tube include both rotating the tube allowing the fin ribbon to be wound thereabout and rotating the fin ribbon about the tube. In those applications wherein the tube is rotated it is common to advance a fin strip from a reel of solid sheet stock and to both slit the fin strip to form perforations to define the projecting fin projections and to form or bend the fin stock to the appropriate configuration for application to the tube. A single continuous fin ribbon normally extends from the reel of fin stock to the tube on which it is wound. The slitting and forming operations are accomplished in a continuous fashion as the fin strip passes along a fin strip route.
It is advantageous to utilize a fin strip of minimum thickness which may be applied at a high rate of speed without breaking. The thickness of the material is minimized to reduce the amount of material necessary to provide a preselected amount of heat transfer. The rate of application is increased to decrease the amount of fin winding machinery necessary to produce a desired quantity of heat exchange surface.
To provide both a minimum thickness of fin stock and a high speed winding operation it is necessary to maintain strict control of the various operations occurring along the fin strip route. By maintaining strict control of the operations sufficient stress to break the fin strip is avoided while sufficient tension to assure the fin strip is wound appropriately about the heat exchange tube is provided. The control described herein provides a cascaded system wherein a master control is utilized to set the speed of a motor driving a rotating tube. Feedback means are used to sense the amount of fin stock between the wrapping location where the fin is wrapped onto the tube and the forming wheels where the fin strip is bent to the appropriate configuration. This feedback means is utilized to generate a signal in combination with the master signal to regulate the speed of the motor driving the forming wheels. In addition thereto the amount of fin stock between the forming wheels and the slitter wheels where the fin strip is perforated to define the fin projections is also determined with a second feedback signal generated in response thereto. This signal is combined with the signal generated from the first feedback means and from the master signal to provide an input to regulate the speed of the motor driving the slitter wheels.